Abstract

Surface-Mounted Permanent-Magnet Synchronous (SMPMS) machine drives have been considered thus far unsuitable for an efficient, wide-range flux weakening operation. This thesis will detail two novel schemes that provide stable and reliable operation over a wide range above the machine base speed, without dependence on machine parameters, usage of look-up tables or DC bus voltage measurements. Both techniques employ space vector modulation (SVM) with the option of smooth transition into six-step mode through the over-modulation range, maximizing the torque available. The first scheme ensures exact torque command tracking, whereas the second one intrinsically gives a steady state error in the flux weakening area. The second method, on the other hand, is computationally simpler, offers better transient response and the steady state torque error is not a critical feature if the torque control loop is an inner loop. The first method uses closed loop control of the phase voltage magnitude to generate magnetizing current reference for the flux-weakening operation. The second approach detects the steady-state error in the torque current component regulation, and then uses the error to generate the magnetizing current reference. However, when the over-modulation and six-step modes are utilized, the fifth and seventh stator current harmonics of the fundamental frequency propagate through the current control loops, resulting in the sixth harmonic in the current error signals and, henceforth, in the reference voltage duty cycles for the flux weakening control section. This deteriorates drive performance. To filter the sixth harmonic, a constrained lattice-structure all-pass-based notch filter is used here, providing minimal phase delay and complete attenuation of the sixth harmonic. Similar filter solutions have been used so far only in certain communications and sonar applications, but this work sets a path for a broader utilization in electrical drive systems. Modeling and simulation techniques, design procedure, and experimental results will be presented. The results of this work proved that SMPMS machines are suitable for applications when the extended speed range was required, e.g., in electric propulsion.